1. Field of the Invention
This invention is related to a gas meter for determining usage of gas products by consumers, and more particularly, to a gas meter having cam-driven reciprocating valve covers.
2. Description of the Related Art
Gas meters have long been used to determine the amount of gas usage by consumers. Particularly where gas flow rates are relatively low such as at the gas inlets of houses and small buildings, for example, diaphragm meters are typically used to measure gas consumption at these locations. Diaphragm meters are usually positioned in an enclosed housing which communicates with a pipe which receives pressurized gas from an external source. Another pipe runs from the diaphragm meter to the inside of the house or building. When a gas burning device such as a stove or furnace is activated, gas begins to flow into the enclosed housing, through the diaphragm meter and into the pipe leading to the activated gas-burning unit. The diaphragm meter measures the amount of gas consumption in the following manner. Initially, a valve cover on the diaphragm meter is in a first position in which gas flows from the enclosed housing into one side of the valve cover through a passage leading to a first side of the diaphragm or bellows enclosed in the diaphragm meter. As the first side expands outward under pressure from the gas flowing from the enclosed housing, gas on the opposite side of the diaphragm is forced toward a second side of the valve cover which guides this gas flow to the inlet pipe via passages defined in the diaphragm meter. The force of this expansion of the first side of the diaphragm also drives a flag coupled to the diaphragm, which rotates a flag axle with an arm attached at one end. The arm forces a meter axle to rotate. The meter axle then rotates dials to indicate the amount of gas usage. The meter axle also has a crank shaft attached to an arm that reciprocates the valve cover so that the valve cover will change position as the diaphragm is driven from its first side. This change in position of the valve cover uncovers another passage which is exposed to the pressurized air in the enclosed housing in which the gas meter sits. The aperture at the second side of the valve cover allows gas to flow to a second side of the diaphragm or bellows and forces it to reciprocate back to its initial position. As the pressurized gas forces the diaphragm to expand in the opposite direction, the gas on the first side of the diaphragm meter is forced out of containment in the diaphragm meter against the valve cover which guides this gas flow toward the pipe leading to the gas-burning unit. The pressurized gas entering the second side of the diaphragm also drives the meter axle via the arm, flag axle and flag attached to the diaphragm.
As previously stated, to reciprocate the valve cover, the meter axle has a crankshaft attached to an arm that is coupled to the valve cover. This crankshaft and its associated components are relatively difficult to manufacture. In addition, the crankshaft is not entirely reliable as it is not driven uniformly throughout the cycle of the diaphragm, but is only driven when the diaphragm is forced in one direction or the other by pressurized gas. Thus, the crankshaft can become stuck, a feature which leads to inaccurate metering of gas consumption and erratic gas flow in the pipe to the gas-burning unit.